Method for controlling exhaust gas heat recovery systems in vehicles

ABSTRACT

A method of operating an exhaust gas heat recovery (EGHR) system in a vehicle including an engine, a transmission, and an EGHR heat exchanger is provided. The method includes monitoring an engine water temperature and may include monitoring a transmission oil temperature and an ambient air temperature. The method includes comparing the monitored engine water temperature to one or more calibrated engine temperatures. Based upon the monitored temperatures and comparison to the calibrated temperatures, the method controls a two-way valve. The two-way valve is configured to be set to one of an engine position and a transmission position. The engine position allows heat-exchange communication between the EGHR heat exchanger and the engine, and the transmission position allows heat-exchange communication between the EGHR heat exchanger, the transmission, and the engine.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with U.S. Government support under Agreement No. PHEV DOE GMT311/166 awarded by the Department of Energy. The U.S. Government may have certain rights in this invention.

TECHNICAL FIELD

This disclosure relates to control of exhaust gas heat reclaim, recovery, or recirculation systems for vehicles.

BACKGROUND

Internal combustion engines produce energy by combustion of a fuel with an (usually) air in a combustion chamber. The combustion process in internal combustion engines produces power to move the vehicle, usually converting the linear motion within the combustion chamber to rotation, but also produces heat.

The combustion products—uncombusted fuel, unused oxygen, and byproducts, in the form of (often) hot exhaust gases—are expelled through an exhaust system taking the combustion products away from the engine. Exhaust gas heat recovery is designed to remove heat from the exhaust gas of engines and transfer it elsewhere, such as to a water circuit. The interior of the car may be warmed using exhaust heat, or thermoelectric devices may produce electricity from the exhaust heat.

SUMMARY

A method of operating an exhaust gas heat recovery (EGHR) system in a vehicle including an engine, a transmission, and an EGHR heat exchanger is provided. The method includes monitoring an engine water temperature and may include monitoring a transmission oil temperature and an ambient air temperature. The method includes comparing the monitored engine water temperature to one or more calibrated engine temperatures. Based upon the monitored temperatures and comparison to the calibrated temperatures, the method controls a two-way valve.

The two-way valve is configured to be set to one of an engine position and a transmission position. The engine position allows heat-exchange communication between the EGHR heat exchanger and the engine, and the transmission position allows heat-exchange communication between the EGHR heat exchanger, the transmission, and the engine.

The method may include comparing the monitored engine water temperature to a calibrated first engine temperature, and if the monitored engine water temperature is below the calibrated first engine temperature, setting the two-way valve to the engine position. The method may further include comparing the monitored transmission oil temperature to a calibrated first transmission temperature, and if the monitored transmission oil temperature is below the calibrated first transmission temperature and the monitored engine water temperature is below the calibrated first engine temperature, setting the two-way valve to the transmission position.

The above features and advantages, and other features and advantages, of the present invention are readily apparent from the following detailed description of some of the best modes and other embodiments for carrying out the invention, as defined in the appended claims, when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an exemplary hybrid vehicle powertrain having an exhaust gas heat recovery (EGHR) system in communication with an engine and a transmission;

FIG. 2 is a schematic flow chart diagram of an algorithm or method for controlling an EGHR system, such as that shown in FIG. 1;

FIG. 3 is a schematic flow chart of a subroutine of the method shown in FIG. 2, showing portions of the method for mild ambient temperatures;

FIG. 4 is a schematic flow chart of another subroutine of the method shown in FIG. 2, showing portions of the method for cold ambient temperatures; and

FIG. 5 is a schematic flow chart of another subroutine of the method shown in FIG. 2, showing portions of the method for extreme or hot ambient temperatures.

DETAILED DESCRIPTION

Referring to the drawings, wherein like reference numbers correspond to like or similar components whenever possible throughout the several figures, there is shown in FIG. 1 a schematic diagram of an exhaust gas heat recovery (EGHR) system, referred to generally as EGHR system 10. The EGHR system 10 is in selective fluid flow and heat-exchange communication with an internal combustion engine 12 and a transmission 14 of a vehicle (not shown).

The engine 12 is drivingly connected to the transmission 14, which may be a hybrid transmission having one or more electric machines (not shown). Alternatively, the vehicle may include one or more electric machines acting directly on the engine output or the transmission input. The engine 12 releases exhaust gas through an exhaust pipe or exhaust system 16, which includes an EGHR heat exchanger 18, as explained herein.

While the present invention is described in detail with respect to automotive applications, those skilled in the art will recognize the broader applicability of the invention. Those having ordinary skill in the art will recognize that terms such as “above,” “below,” “upward,” “downward,” et cetera, are used descriptively of the figures, and do not represent limitations on the scope of the invention, as defined by the appended claims.

FIG. 1 shows a highly-schematic control architecture or control system 20 for the EGHR system 10. The control system 20 may include one or more components (not separately shown) with a storage medium and a suitable amount of programmable memory, which are capable of storing and executing one or more algorithms or methods to effect control of the EGHR system 10. Each component of the control system 20 may include distributed controller architecture, such as a microprocessor-based electronic control unit (ECU). Additional modules or processors may be present within the control system 20.

An engine water circuit 22 moves coolant or water from the engine 12 through, eventually, the EGHR heat exchanger 18. The engine water circuit 22 is supplied with pressurized coolant by a primary pump (not separately shown) incorporated with the engine 12. The primary pump may be a mechanical pump driven by rotation of the engine 12. Depending upon the operating conditions of the EGHR system 10, the coolant in the engine water circuit 22 may be heated by the exhaust gases from the engine 12. A transmission water circuit 24 is selectively connected to the engine water circuit 22 by a two-way valve 26, which allows heat-flow or heat-exchange communication between the transmission water circuit 24 and the engine water circuit 22.

The two-way valve 26 is configured to be selectively controlled or set to one of an engine position and a transmission position. The engine position of the two-way valve 26 allows heat-exchange communication between the EGHR heat exchanger 18 and the engine 12. The transmission position allows heat-exchange communication between the EGHR heat exchanger 18 and both the transmission 14 and the engine 12. When the two-way valve 26 is in the transmission position, the transmission water circuit 24 is supplied with coolant or water from the engine water circuit 22 by the primary pump, if the primary pump is operating. A transmission oil circuit 28 circulates lubricating and cooling oil from the transmission 14. The two-way valve 26 may be electrically operated, fluid operated (such as by a pilot valve), or operated in any suitable manner to move between the engine position and the transmission position.

The exact boundaries and paths of the engine water circuit 22 and the transmission water circuit 24 may vary slightly. The engine water circuit 22 provides communication between the engine 12 and the EGHR heat exchanger 18. The transmission water circuit 24 provides communication between the engine water circuit 22 and the transmission oil circuit 28. The two-way valve 26 has three ports: a first port or inlet port brings water or coolant in from the heater core 30 or directly from the coolant outlet of the engine 12; a second port links the inlet flow to the engine water circuit 22 such that only the engine water circuit 22 has flow; and a third port links the inlet flow to the transmission water circuit 24.

In addition to the EGHR heat exchanger 18, the EGHR system 10 includes other heat exchangers or radiators. A heater core 30 allows heat to be transferred from the coolant or water leaving the engine 12 to the cabin (passenger compartment) of the vehicle. An engine radiator 32 is a water-to-air heat exchanger configured to selectively dissipate heat from the engine 12 to ambient air flowing through the engine radiator 32. A thermostat (not shown) may be used to control flow of coolant from the engine 12 through the engine radiator 32. A transmission radiator 34 is an oil-to-air heat exchanger configured to selectively dissipate heat from the transmission oil circuit 28 of the transmission 14 to ambient air flowing through the transmission radiator 34.

While the engine radiator 32 and the transmission radiator 34 are shown schematically side-by-side, in many applications of the EGHR system 10, the engine radiator 32 and transmission radiator 34 would be placed one in front of the other at an area of high airflow into the underhood area of the vehicle. However, the engine radiator 32 and the transmission radiator 34 may be located elsewhere in the vehicle. As used herein, heat exchanger may refer to myriad different devices for exchanging heat energy between two mediums or two systems.

The actual direction of flow of heat energy between any sides of a heat exchanger is controlled by temperature difference across the specific heat exchanger. For example, if the engine 12 were very cold and the thermostat allowed circulation through the engine radiator 32 on a very hot day, the engine radiator 32 would warm the coolant until it reached (approximately) the ambient temperature and would then cool the engine coolant when the coolant temperature exceeded the ambient temperature.

A central heat exchanger 36 is an oil-to-water heat exchanger which allows heat-exchange communication between the transmission oil circuit 28 of the transmission 14 and the transmission water circuit 24. The central heat exchanger 36 allows heat to be transferred from the transmission water circuit 24 to the transmission oil circuit 28 in order to warm the transmission 14 and reduce slip loss. Furthermore, as discussed herein, the central heat exchanger 36 also allows the transmission 14 and transmission radiator 34 to dissipate excess heat from the engine 12 during hot or extreme conditions.

An auxiliary pump 38 is disposed within the engine water circuit 22. The auxiliary pump 38 may be used to add pressure and increase flow through the engine water circuit 22 and, selectively, the transmission water circuit 24 when the need arises. Furthermore, when the engine 12 is turned off or un-fueled by the hybrid vehicle controls (not shown separately) the auxiliary pump 38 may be used as the main pressure source for the engine water circuit 22 and the transmission water circuit 24. Therefore, the auxiliary pump 38 may be used to supplement the primary pump incorporated into the engine 12, may be used as the only pump when the engine 12 and the primary pump are not operating, or may be used as the sole pump for the engine water circuit 22 and the transmission water circuit 24.

An EGHR bypass valve 42 controls flow of exhaust gases through the EGHR heat exchanger 18. The EGHR bypass valve 42 is shown in its non-bypass position, which allows flow of exhaust gases through the EGHR heat exchanger 18 and allows heat-exchange communication between the exhaust gases and the engine water circuit 22. When the EGHR bypass valve 42 is switched, flipped, or otherwise actuated to a bypass position—shown in FIG. 1 as a dashed line and labeled as element 43—exhaust gases leaving the engine 12 are not allowed to pass through the EGHR heat exchanger 18.

The EGHR bypass valve 42 may be controlled by a solenoid, a mechanical thermostat, a wax motor, vacuum actuator, or other suitable controls, and may be switched between the non-bypass position and the bypass position at varying temperatures and conditions. The EGHR bypass valve 42 may be controlled based upon the monitored engine temperature or based upon the temperature of the coolant flowing through the EGHR heat exchanger 18. For example, and without limitation, the EGHR bypass valve 42 may be a wax motor driven by coolant temperatures of seventy-two degrees Celsius or greater in the engine water circuit 22. The set-point temperature for the EGHR bypass valve 42, and other settings within the EGHR system 10, is exemplary and illustrative only. The specific values for set points will be determined based upon the specific configuration of the EGHR system 10 and the vehicle into which it is incorporated.

A transmission thermostat 44 controls flow between the transmission oil circuit 28 and the transmission radiator 34. The transmission thermostat 44 is shown in its direct return position, which directs flow of exhaust returning from the central heat exchanger 36 back to the transmission 14 without passing through the transmission radiator 34. When the transmission thermostat 44 is switched, flipped, or otherwise actuated to a radiator position—shown in FIG. 1 as a dashed line and labeled as element 45—oil returning from the central heat exchanger 36 is directed through the transmission radiator 34 before returning to the transmission 14.

When the transmission thermostat 44 is in the radiator position (as shown as 45 in FIG. 1) heat may be transferred or communicated from either the transmission 14 or the central heat exchanger 36 to the ambient air via the transmission radiator 34. For example, and without limitation, the transmission thermostat 44 may be a mechanical or an electromechanical thermostat opened by oil temperatures greater than eighty-two degrees Celsius or greater than ninety-two degrees Celsius in the transmission oil circuit 28, depending upon the size of the transmission radiator 34.

Flow arrows are shown in FIG. 1 in order to illustrate the path and direction of flow through some areas and components of the EGHR system 10 during specific operating modes. The EGHR bypass valve 42 is shown in the non-bypass modes so that exhaust gases are flowing through the EGHR heat exchanger 18. The transmission thermostat 44 is shown in the direct return position so that oil is not passing through the transmission radiator 34. The two-way valve 26 is shown in the transmission position so that the transmission water circuit 24 is in fluid communication with the engine water circuit 22. When the two-way valve 26 is in the transmission position the central heat exchanger 36 allows heat-exchange communication between the engine water circuit 22 (via the transmission water circuit 24) and the transmission oil circuit 28.

An ambient air sensor 46 monitors the temperature of the ambient air around (and flowing through) the vehicle and is in communication with the control system 20. Either the control system 20 or the ambient air sensor 46 compares the monitored ambient air temperature to one of a calibrated cold ambient temperature, a calibrated mild ambient temperature, and a calibrated hot ambient temperature. Each of the calibrated temperatures referred to herein may be determined through testing or modeling of the EGHR system 10 and the vehicle. Furthermore, the calibrated temperatures may be altered throughout the lifetime of the vehicle based upon the lifecycle of the vehicle or components thereof or based upon learned operating characteristics of the vehicle of having the EGHR system 10. The values given for the calibrated temperatures are illustrative and exemplary only, and the values are not intended to limit the scope of the invention unless included in the claims defining the invention.

Referring now to FIGS. 2-5, and with continued reference to FIG. 1, there are shown schematic flow chart diagrams of an algorithm or method 200 for controlling exhaust gas heat recovery, such as the EGHR system 10 shown in FIG. 1. The exact order of the steps of the algorithm or method 200 shown in FIGS. 2-5 is not required. Steps may be reordered, steps may be omitted, and additional steps may be included. Furthermore, the method 200 may be a portion or sub-routine of another algorithm or method.

For illustrative purposes, the method 200 may be described with reference to the elements and components shown and described in relation to FIG. 1 and may be executed by the control system 20. However, other components may be used to practice the method 200 and the invention defined in the appended claims. Any of the steps may be executed by multiple components within the control system 20.

FIG. 2 shows a high-level diagram of the method 200. FIG. 3 shows a mild sub-routine 300 of the method 200 occurring during mild ambient temperatures; FIG. 4 shows a cold sub-routine 400 of the method 200 occurring during cold ambient temperatures; and FIG. 5 shows a hot sub-routine 500 of the method 200 occurring during hot ambient temperatures.

Step 210: Start.

The method 200 may begin at a start or initialization step, during which time the method 200 is monitoring operating conditions of the vehicle and of the EGHR system 10. Initiation may occur in response to the vehicle operator inserting the ignition key or in response to specific conditions being met, such as in response to a negative torque request (braking or deceleration request) from the driver or cruise control module combined with a predicted or commanded downshift. Alternatively, the method 200 may be running constantly or looping constantly whenever the vehicle is in use.

Step 212: Determine Ambient, Transmission, and Engine Temperatures.

The method 200 includes monitoring or determining temperatures of different components or conditions. An ambient air temperature is monitored, such as with the ambient air sensor 46. An engine water temperature is also monitored. The engine water temperature may be determined from within the engine 12, at the entrance to the engine water circuit 22, or from another location of the engine water circuit 22. A transmission oil temperature is also monitored. The transmission oil temperature may be determined from within the transmission 14, at the entrance to the transmission oil circuit 28, or from another location.

Step 214: Compare Ambient Air to Calibrated Temperatures.

The method 200 compares the monitored ambient air temperature to the calibrated cold ambient temperature, the calibrated mild ambient temperature, and the calibrated hot ambient temperature to determine the ambient air temperature range. For example, and without limitation, the calibrated cold ambient temperature may be any monitored ambient temperature below eight degrees Celsius; the calibrated mild ambient temperature may be any monitored ambient temperature between eight and seventeen degrees Celsius; and the calibrated hot ambient temperature may be any monitored ambient temperature above seventeen degrees Celsius.

If the method 200 determines that the temperature is within the mild range, the method 200 proceeds to the mild sub-routine 300. If the method 200 determines that the temperature is within the cold range, the method 200 proceeds to the cold sub-routine 400. If the method 200 determines that the temperature is within the hot range, the method 200 proceeds to the hold sub-routine 500.

Mild Sub-Routine 300.

Referring now to FIG. 3, and with continued reference to FIGS. 1-2, there is shown a schematic flow chart diagram of the mild sub-routine 300. The mild sub-routine 300 is a portion of the method 200 shown in FIG. 2 and is represented in FIG. 2 as a part of the block denoted by the number 300. The steps shown in the flow chart diagram of FIG. 3 may be only a portion of the mild sub-routine 300, such that the method 200 may include further steps within the mild sub-routine 300. The mild temperature range occurs when the ambient air temperature is monitored to be between the cold temperature range and the hot temperature range.

Step 310: Engine Temperature Less than Calibrated First Temperature?

The method 200 includes comparing the monitored engine water temperature to a calibrated first engine temperature. For example, and without limitation, the calibrated first engine temperature may be approximately sixty degrees Celsius.

As viewed in FIGS. 3-5, basic decision steps answered positively (as a yes) follow the path labeled with a “+” sign (the mathematical plus or addition operator). Similarly, decision steps answered negatively (as a no) follow the path labeled with a “−” sign (the mathematical minus or subtraction operator).

Step 312: Engine-Warming Mode.

If the method 200 determines that the monitored engine water temperature is below the calibrated first engine temperature, the method 200 proceeds to an engine-warming mode for the EGHR system 10. Depending upon the configuration of the engine 12, operating below the calibrated first engine temperature may affect fuel efficiency. Therefore, the method 200 places the EGHR system 10 into the engine-warming mode to increase the temperature of the engine 12 with any available heat from the exhaust gases through the EGHR heat exchanger 18.

Step 314: Valve Set to Engine Position.

If the monitored engine water temperature is below the calibrated first engine temperature, then execution of the engine-warming mode includes controlling (setting) the two-way valve 26 to the engine position. The control system 20 may actuate the two-way valve 26 based upon the determination of the method 200. Furthermore, the EGHR bypass valve 42 is calibrated to remain in the non-bypass position because the temperature of the coolant passing through the engine water circuit 22 is insufficient to actuate or trigger the bypass valve.

When in the engine-warming mode, hot exhaust gases travel through the exhaust system 16 and are directed through the EGHR heat exchanger 18 by the EGHR bypass valve 42. Coolant leaves the engine 12 and passes through the heater core 30. The two-way valve 26 prevents flow of the coolant through the transmission water circuit 24, so the coolant is circulated only through the engine water circuit 22. The exhaust gases transfer heat to the coolant in the engine water circuit 22, which returns to the engine 12 and warms the engine 12.

Although the transmission water circuit 24 has no flow, the transmission oil circuit 28 may be circulating oil through the central heat exchanger 36. The temperature of the transmission 14 is substantially controlled by heat generated within the transmission 14 and by heat dissipated through the transmission radiator 34 if the transmission thermostat 44 moves to the radiator position.

The method 200 may stay in engine-warming mode with the two-way valve 26 set to the engine position for a pre-determined or a calculated time period. However, the method 200 may be looping or iterating repeatedly and the engine-warming mode may continue until a subsequent loop determines that conditions of the EGHR system 10 have changed, and the method 200 results in another operating mode.

Step 316: Transmission Temperature Less than Calibrated First Temperature?

If the method 200 determines that the monitored transmission oil temperature is at or above (i.e. not below) the calibrated first engine temperature, then the method 200 does not need to enter the engine-warming mode. The method 200 then includes comparing the monitored transmission oil temperature to a calibrated first transmission temperature. For example, and without limitation, the calibrated first transmission temperature may be approximately eighty degrees Celsius.

Depending upon the configuration of the transmission 14, operating below the calibrated first transmission temperature may affect fuel efficiency. However, the transmission 14 may be negatively effected if the monitored transmission oil temperature too hot.

Step 318: Transmission-Warming Mode.

If the monitored transmission oil temperature is below the calibrated first transmission temperature and the monitored engine water temperature is below the calibrated first engine temperature, then the method 200 will control the EGHR system 10 to a transmission-warming mode. In the transmission-warming mode, heat from the engine 12, the EGHR heat exchanger 18, or both, is transferred through the central heat exchanger 36 to the transmission oil circuit 28 and the transmission 14.

Step 320: Valve Set to Transmission Position.

When in the transmission-warming mode, the method 200 includes setting the two-way valve 26 to the transmission position. When the two-way valve 26 is in the transmission position, coolant passes through the heater core 30 and is then directed through the transmission water circuit 24 and the central heat exchanger 36 before proceeding to the EGHR heat exchanger 18 and back to the engine 12. Any time that the EGHR system 10 is in the transmission-warming mode, the two-way valve 26 will be set to the transmission position.

During the transmission-warming mode, heat from the engine 12 will be transferred through the central heat exchanger 36 to the transmission 14. Furthermore, heat from the exhaust gases will transfer from the EGHR heat exchanger 18 to the engine water circuit 22 to either raise the temperature of engine 12 or to replenish the heat transferred to the transmission 14. If the temperature of the engine rises substantially during the transmission-warming mode, the EGHR bypass valve 42 will close (driven by, for example, the wax motor) to the bypass position (shown as 43 in FIG. 1) and prevent heat from exhaust gases from passing to the engine water circuit 22. The transmission-warming mode is shown in FIG. 1 where the two-way valve 26 is allowing heat-exchange communication between the EGHR heat exchanger 18, the engine 12, and the transmission 14.

Like the engine-warming mode, the method 200 may stay in transmission-warming mode with the two-way valve 26 set to the transmission position for a pre-determined or a calculated time period. However, the method 200 may be looping or iterating repeatedly and the transmission-warming mode may continue until a subsequent loop determines that conditions of the EGHR system 10 have changed, and the method 200 results in another operating mode. Whenever the EGHR system 10 is in the transmission-warming mode, the two-way valve 26 will be set to the transmission position.

Step 322: Transmission Cooling Mode.

If the monitored transmission oil temperature is above the calibrated first transmission temperature and the monitored engine water temperature is below the calibrated first engine temperature, then the method 200 will control the EGHR system 10 to a transmission cooling mode. In the transmission cooling mode, heat from the transmission 14 is either retained within the transmission oil circuit 28 or dissipated through the transmission radiator 34.

Step 324: Valve Set to Engine Position.

When in the transmission cooling mode, the method 200 includes setting the two-way valve 26 to the engine position. When the two-way valve 26 is in the engine position, no coolant flow occurs in the transmission water circuit 24. Therefore, heat is not exchanged through the central heat exchanger 36 to the transmission 14.

During the transmission cooling mode, coolant continues to flow through the engine water circuit 22 and the temperature of the engine 12 will be controlled solely by the EGHR bypass valve 42. Oil continues to circulate through the transmission oil circuit 28. However, because no coolant is flowing through the central heat exchanger 36, no heat will be transferred to the transmission 14. If the temperature of the transmission 14 rises above the level necessary to actuate or trigger the transmission thermostat 44, fluid will flow through the transmission radiator 34 and dissipate heat from the transmission oil circuit 28, thereby cooling the transmission 14.

Cold Sub-Routine 400.

Referring now to FIG. 4, and with continued reference to FIGS. 1-3, there is shown a schematic flow chart diagram of the cold sub-routine 400. The cold sub-routine 400 is a portion of the method 200 shown in FIG. 2 and is represented in FIG. 2 as a part of the block denoted by the number 400. The steps shown in the flow chart diagram of FIG. 4 may be only a portion of the cold sub-routine 400, such that the method 200 may include further steps within the cold sub-routine 400. The cold temperature range occurs below the mild temperature range. The cold sub-routine 400 may be called-up whenever the method 200 determines that the ambient temperature is below the calibrated cold ambient temperature.

Step 410: Engine Temperature Less than Calibrated Second Temperature?

If the monitored ambient air temperature is below the calibrated cold ambient temperature, the method 200 includes comparing the monitored engine water temperature to a calibrated second engine temperature. The calibrated second engine temperature may be the same as or different from the calibrated first engine temperature. For example, and without limitation, the calibrated second engine temperature may be approximately seventy-five degrees Celsius, while calibrated first engine temperature is sixty degrees Celsius. The calibrated second engine temperature may be greater than the calibrated first engine temperature because the relatively colder ambient air temperature provides less heat to the engine 12.

Step 412: Engine-Warming Mode.

If the method 200 determines that the monitored engine water temperature is below the calibrated second engine temperature, the method 200 proceeds to the engine-warming mode for the EGHR system 10. The method 200 places the EGHR system 10 into the engine-warming mode to increase the temperature of the engine 12—if any heat is available from the exhaust gases—through the EGHR heat exchanger 18.

Step 414: Valve Set to Engine Position.

Executing the engine-warming mode includes controlling or setting the two-way valve 26 to the engine position. The control system 20 may actuate the two-way valve 26 based upon the determination of the method 200. Furthermore, the EGHR bypass valve 42 is calibrated to remain in the non-bypass position because the temperature of the coolant passing through the engine water circuit 22 is insufficient to actuate or trigger the bypass valve.

As during the engine-warming mode of the mild ambient sub-routine 300 shown in FIG. 3, when the EGHR system 10 is in the engine-warming mode, hot exhaust gases travel through the exhaust system 16 and are directed through the EGHR heat exchanger 18 by the EGHR bypass valve 42. Coolant leaves the engine 12, passes through the heater core 30, and the two-way valve 26 prevents flow of the coolant through the transmission water circuit 24. The coolant is circulated only through the engine water circuit 22. The exhaust gases transfer heat to the coolant in the engine water circuit 22, which returns to warm the engine 12.

Step 416: Engine Producing Positive Torque?

If the method 200 determines that the monitored engine water temperature is not below the calibrated second engine temperature, the method 200 proceeds to monitoring for an auto-stop mode. Auto-stop mode occurs when vehicles shut down, power off, or cut fuel to the engine 12. Alternatively stated, auto-stop mode occurs when the engine 12 is not producing positive torque.

Step 418: Transmission-Warming Mode.

If the engine 12 is not in auto-stop mode, such that the engine 12 is producing positive torque, then the method 200 will control the EGHR system 10 to the transmission-warming mode. In the transmission-warming mode, during cold ambient temperatures, heat from the engine 12, residual heat from the EGHR heat exchanger 18, or heat from both, is transferred through the central heat exchanger 36 to the transmission oil circuit 28 and the transmission 14.

Step 420: Valve Set to Transmission Position.

When in the transmission-warming mode, the method 200 sets the two-way valve 26 to the transmission position. When the two-way valve 26 is in the transmission position, coolant passes through the heater core 30 and is then directed through the transmission water circuit 24 and the central heat exchanger 36 before proceeding to the EGHR heat exchanger 18 and back to the engine 12. Any time that the EGHR system 10 is in the transmission-warming mode, the two-way valve 26 will be set to the transmission position.

During the transmission-warming mode, heat from the engine 12 will be transferred through the central heat exchanger 36 to the transmission 14. Furthermore, heat from the exhaust gases left in the EGHR heat exchanger 18 will transfer from the EGHR heat exchanger 18 to the engine water circuit 22 and eventually to the transmission 14.

Step 422: Auto-Stop Mode.

If the engine 12 is in the auto-stop mode, the engine 12 is not producing torque and is likely not producing heat. Furthermore, during the auto-stop mode, the auxiliary pump 38 will be turned on to provide pressure to the engine water circuit 22 and, if connected by the two-way valve 26, to the transmission water circuit 24.

Step 424: Transmission Temperature Less than Calibrated Second Temperature?

After determining that the engine 12 is in auto-stop mode, the method 200 then includes comparing the monitored transmission oil temperature to a calibrated second transmission temperature. For example, and without limitation, the calibrated second transmission temperature may be approximately seventy degrees Celsius, which is lower than the first calibrated transmission temperature used in the mild ambient temperature sub-routine 300.

Step 426: Transmission-Warming Mode.

If the engine 12 is in auto-stop mode and the monitored transmission oil temperature is below the calibrated second transmission temperature, then the method 200 will again control the EGHR system 10 to the transmission-warming mode. In the transmission-warming mode, during cold ambient temperatures, heat from the engine 12, residual heat from the EGHR heat exchanger 18, or heat from both, is transferred through the central heat exchanger 36 to the transmission oil circuit 28 and the transmission 14.

Step 428: Valve Set to Transmission Position.

When in the transmission-warming mode, the method 200 sets the two-way valve 26 to the transmission position. When the two-way valve 26 is in the transmission position, coolant passes through the heater core 30 and is then directed through the transmission water circuit 24 and the central heat exchanger 36 before proceeding to the EGHR heat exchanger 18 and back to the engine 12.

During the transmission-warming mode, heat from the engine 12 will be transferred through the central heat exchanger 36 to the transmission 14. Furthermore, heat from the exhaust gases left in the EGHR heat exchanger 18 will transfer from the EGHR heat exchanger 18 to the engine water circuit 22 and eventually to the transmission 14.

Step 430: Engine-Warming Mode.

If the method 200 determines that the engine 12 is in the auto-stop mode (not producing torque) and if the monitored transmission oil temperature is not below the calibrated second transmission temperature, the method 200 proceeds to the engine-warming mode for the EGHR system 10. The method 200 places the EGHR system 10 into the engine-warming mode to increase the temperature of the engine 12—if any heat is available from the exhaust gases—through the EGHR heat exchanger 18. During auto-stop mode, additional heat in the transmission 14 may be used as additional thermal mass to delay the next engine-on event if the transmission 14 is above the calibrated second transmission temperature.

Step 432: Valve Set to Engine Position.

Executing the engine-warming mode includes controlling or setting the two-way valve 26 to the engine position. When the EGHR system 10 is in the engine-warming mode, residual heat from hot exhaust gases is directed through the EGHR heat exchanger 18 by the EGHR bypass valve 42. Coolant leaves the engine 12, passes through the heater core 30, and the two-way valve 26 prevents flow of the coolant through the transmission water circuit 24. The exhaust gases transfer heat to the coolant in the engine water circuit 22, which returns to warm the engine 12.

Hot Sub-Routine 500.

Referring now to FIG. 5, and with continued reference to FIGS. 1-4, there is shown a schematic flow chart diagram of the hot sub-routine 500. The hot sub-routine 500 is a portion of the method 200 shown in FIG. 2 and is represented in FIG. 2 as a part of the block denoted by the number 500. The steps shown in the flow chart diagram of FIG. 5 may be only a portion of the hot sub-routine 500, such that the method 200 may include further steps within the hot sub-routine 500. The hot temperature range occurs above the mild temperature range.

The hot sub-routine 500 may be called-up whenever the method 200 determines that the ambient temperature is above the calibrated hot ambient temperature. When the ambient air temperature is in the hot range, the potential for heat degradation or damage to the engine 12 or the transmission 14 is increased.

Step 510: Transmission Temperature Less than Calibrated First Temperature?

The method 200 again includes comparing the monitored transmission oil temperature to the calibrated first transmission temperature. If the monitored transmission oil temperature is below the calibrated first transmission temperature, then the transmission 14 is cold—even though the ambient temperature is hot—and efficiency may be reduced.

Step 512: Transmission-Warming Mode.

If the monitored transmission oil temperature is below the calibrated first transmission temperature and the monitored ambient air temperature is above the calibrated hot ambient temperature, then the method 200 will control the EGHR system 10 to a transmission-warming mode. As in other ambient air temperatures, such as those shown in FIGS. 3 and 4, when the EGHR system 10 is in the transmission-warming mode, heat from the engine 12 or from the EGHR heat exchanger 18, or both, is transferred through the central heat exchanger 36 to the transmission oil circuit 28 and the transmission 14.

Step 514: Valve Set to Transmission Position.

When in the transmission-warming mode, the method 200 includes setting the two-way valve 26 to the transmission position. When the two-way valve 26 is in the transmission position, coolant passes through the heater core 30 and is then directed through the transmission water circuit 24 and the central heat exchanger 36 before proceeding to the EGHR heat exchanger 18 and back to the engine 12. Any time that the EGHR system 10 is in the transmission-warming mode, the two-way valve 26 will be set to the transmission position.

During the transmission-warming mode, heat from the engine 12 will be transferred through the central heat exchanger 36 to the transmission 14. Furthermore, heat from the exhaust gases will transfer from the EGHR heat exchanger 18 to the engine water circuit 22 to either raise the temperature of engine 12 or to replenish the heat transferred to the transmission 14. If the temperature of the engine rises substantially during the transmission-warming mode, the EGHR bypass valve 42 will close (driven by, for example, the wax motor) to the bypass position (shown as 43 in FIG. 1) and prevent heat from exhaust gases from passing to the engine water circuit 22.

Step 516: Transmission Temperature not Cold.

If the monitored transmission oil temperature is not below the calibrated first transmission temperature, then the method 200 does not need to warm the transmission 14. The method 200 may then determine whether either the engine 12 or the transmission 14 is experiencing extremely high temperatures.

Step 518: Engine Temperature Less than Calibrated Extreme Temperature?

The method 200 includes comparing the monitored engine water temperature to a calibrated extreme engine temperature or a calibrated third engine temperature. The calibrated extreme engine temperature may be based upon temperatures above which the engine 12 is likely to degrade, if maintained for an extended period of time. For example, and without limitation, the calibrated extreme engine temperature may be approximately one hundred twenty degrees Celsius.

Step 520: Engine Temperature not Extreme.

If the method 200 determines that the monitored engine water temperature is less than the calibrated extreme engine temperature, then the engine 12 is not experiencing extreme temperatures. However, although warming of the engine 12 may not be needed, the method 200 then sets the two-way valve 26 to the engine position.

Step 522: Valve Set to Engine Position.

When the two-way valve 26 is set to the engine position, the temperature of the engine 12 may warm, cool, or stay relatively constant. If the temperature of the coolant in the engine water circuit 22 is below the temperature necessary to actuate the EGHR bypass valve 42, heat will be transferred from the exhaust gases to the engine 12. However, if the temperature is above the level necessary to close the EGHR bypass valve 42—by actuating, for example, the wax motor—to the bypass position (shown as 43 in FIG. 1), exhaust gases will be prevented from passing to the engine water circuit 22. Note also that high temperatures within the engine 12 may trigger the engine thermostat to begin flow through the engine radiator 32 to cool the engine 12.

Step 524: Transmission Temperature Less than Calibrated Extreme Temperature?

If the monitored engine water temperature is greater than the calibrated extreme engine temperature, then the engine 12 is experiencing extreme temperatures. The method 200 then proceeds to determine whether the excess heat in the engine 12 may be dissipated through the transmission 14 and the transmission radiator 34. Therefore, the method 200 includes comparing the monitored transmission oil temperature to a calibrated extreme transmission temperature.

The calibrated extreme transmission temperature may be based upon temperatures above which the transmission 14 is likely to degrade, if maintained for an extended period of time. For example, and without limitation, the calibrated extreme transmission temperature may be approximately one hundred ten degrees Celsius. Note that when the temperature of the engine 12 is above the calibrated extreme engine temperature, the engine thermostat is likely allowing flow through the engine radiator 32 and the EGHR bypass valve 42 is in the bypass position (shown as dashed line 43 in FIG. 1).

Step 526: Engine Cooling Through the Transmission.

If the monitored transmission oil temperature is below the calibrated extreme transmission temperature while the monitored engine water temperature is greater than the calibrated extreme engine temperature, then there is excess cooling capacity through the transmission 14. Excess heat from the engine 12 may be transferred from the engine 12 to the transmission oil circuit 28 and the transmission radiator 34.

Step 528: Valve Set to Transmission Position.

The method 200 includes setting the two-way valve 26 to the transmission position, such that the transmission radiator 34 is in heat-exchange communication with the engine 12. Heat is transferred from the engine 12 to the engine water circuit 22 and through the central heat exchanger 36 to the transmission oil circuit 28.

If the temperature of the transmission oil circuit 28 rises above the level necessary to actuate the transmission thermostat 44 to the radiator position (shown as dashed line 45 in FIG. 1). Once the transmission thermostat 44 allows flow through the transmission radiator 34, the excess heat transferred from the engine 12 is dissipated through the transmission radiator 34. By setting the two-way valve 26 to the transmission position, this configuration of the EGHR system 10 allows excess heat from the engine 12 to be dissipated through the transmission 14 and the transmission radiator 34.

Therefore, in certain conditions, the EGHR systems 10 may be placed into engine-warming, engine-cooling, transmission-warming, or transmission-cooling modes. The vehicle cabin may also be warmed through the heater core 30. Operation of the EGHR system 10 in the various modes is controlled by selection of the position of the two-way valve 26 based upon monitored or determined temperatures of the ambient air, the engine 12, or the transmission 14.

Step 530: No Excess Cooling Capacity.

If the monitored engine water temperature is greater than the calibrated extreme engine temperature and the monitored transmission oil temperature is also greater than the calibrated extreme transmission temperature, there is no excess cooling capacity available through the transmission 14 or transmission radiator 34.

Step 532: Valve Set to Engine Position.

The method then sets the two-way valve 26 to the engine position, such that the transmission radiator 34 is not in heat-exchange communication with the engine 12. Therefore, the EGHR system 10 is configured to only transfer heat to the transmission 14 when it is below the calibrated extreme transmission temperature. When both the engine 12 and the transmission 14 are above their respective extreme temperatures, the engine radiator 32 and the transmission radiator 34 are used to dissipate heat.

The detailed description and the drawings or figures are supportive and descriptive of the invention, but the scope of the invention is defined solely by the claims. While some of the best modes and other embodiments for carrying out the claimed invention have been described in detail, various alternative designs and embodiments exist for practicing the invention defined in the appended claims. 

1. A method of operating an exhaust gas heat recovery (EGHR) system in a vehicle including an engine, a transmission, and an EGHR heat exchanger, the method comprising: controlling a two-way valve, wherein the two-way valve is configured to be set to one of an engine position and a transmission position, wherein the engine position allows heat-exchange communication between the EGHR heat exchanger and the engine and the transmission position allows heat-exchange communication between the EGHR heat exchanger, the transmission, and the engine; monitoring an engine water temperature; comparing the monitored engine water temperature to a calibrated first engine temperature; and if the monitored engine water temperature is below the calibrated first engine temperature, setting the two-way valve to the engine position.
 2. The method of claim 1, further comprising: monitoring a transmission oil temperature; comparing the monitored transmission oil temperature to a calibrated first transmission temperature; and if the monitored transmission oil temperature is below the calibrated first transmission temperature and the monitored engine water temperature is below the calibrated first engine temperature, setting the two-way valve to the transmission position.
 3. The method of claim 2, further comprising: monitoring an ambient air temperature; comparing the monitored ambient air temperature to a calibrated hot ambient temperature; if the monitored ambient air temperature is greater than the calibrated hot ambient temperature, comparing the monitored engine water temperature to a calibrated extreme engine temperature; and if the monitored engine water temperature is less than the calibrated extreme engine temperature, setting the two-way valve to the engine position.
 4. The method of claim 3, wherein the vehicle further includes a transmission radiator, and further comprising: if the monitored engine water temperature is greater than the calibrated extreme engine temperature, comparing the monitored transmission oil temperature to a calibrated extreme transmission temperature; and if the monitored transmission oil temperature is below the calibrated extreme transmission temperature, setting the two-way valve to the transmission position, such that the transmission radiator is in heat-exchange communication with the engine.
 5. The method of claim 4, further comprising: if the monitored engine water temperature is greater than the calibrated extreme engine temperature and the monitored transmission oil temperature is greater than the calibrated extreme transmission temperature, setting the two-way valve to the engine position, such that the transmission radiator is not in heat-exchange communication with the engine.
 6. The method of claim 5, further comprising: comparing the monitored ambient air temperature to one of a calibrated cold ambient temperature, a calibrated mild ambient temperature, and the calibrated hot ambient temperature; if the monitored ambient air temperature is below the calibrated cold ambient temperature, comparing the monitored engine water temperature to a calibrated second engine temperature, wherein the calibrated second engine temperature is greater than the calibrated first engine temperature; and if the monitored engine water temperature is below the calibrated second engine temperature, setting the two-way valve to the engine position.
 7. The method of claim 6, further comprising: monitoring for an auto-stop mode, wherein the auto-stop mode occurs when the engine is not producing positive torque; if the engine is in the auto-stop mode and if the monitored ambient air temperature is below the calibrated cold ambient temperature, comparing the monitored transmission oil temperature to a calibrated second transmission temperature, wherein the calibrated second transmission temperature is less than the calibrated first transmission temperature; and if the monitored transmission oil temperature is below the calibrated second transmission temperature, setting the two-way valve to the transmission position.
 8. The method of claim 7, wherein the calibrated hot ambient temperature is seventeen degrees Celsius.
 9. The method of claim 8, wherein the calibrated cold ambient temperature is eight degrees Celsius.
 10. A method of operating an exhaust gas heat recovery (EGHR) system in a vehicle including an engine, a transmission, a transmission radiator, and an EGHR heat exchanger, the method comprising: controlling a two-way valve, wherein the two-way valve is configured to be set to one of an engine position and a transmission position, wherein the engine position allows heat-exchange communication between the EGHR heat exchanger and the engine and the transmission position allows heat-exchange communication between the EGHR heat exchanger, the transmission, and the engine; monitoring an engine water temperature; monitoring a transmission oil temperature; monitoring an ambient air temperature; and comparing the monitored ambient air temperature to a calibrated hot ambient temperature, and: if the monitored ambient air temperature is greater than the calibrated hot ambient temperature, comparing the monitored engine water temperature to a calibrated extreme engine temperature, if the monitored engine water temperature is less than the calibrated extreme engine temperature, setting the two-way valve to the engine position, if the monitored engine water temperature is greater than the calibrated extreme engine temperature, comparing the monitored transmission oil temperature to a calibrated extreme transmission temperature, and if the monitored transmission oil temperature is below the calibrated extreme transmission temperature, setting the two-way valve to the transmission position, such that the transmission radiator is in heat-exchange communication with the engine.
 11. The method of claim 10, further comprising: if the monitored engine water temperature is greater than the calibrated extreme engine temperature and the monitored transmission oil temperature is greater than the calibrated extreme transmission temperature, setting the two-way valve to the engine position, such that the transmission radiator is not in heat-exchange communication with the engine.
 12. The method of claim 11, further comprising: comparing the monitored ambient air temperature to one of a calibrated cold ambient temperature, a calibrated mild ambient temperature, and the calibrated hot ambient temperature; if the monitored ambient air temperature is below the calibrated cold ambient temperature, comparing the monitored engine water temperature to a calibrated second engine temperature, wherein the calibrated second engine temperature is greater than the calibrated first engine temperature; and if the monitored engine water temperature is below the calibrated second engine temperature, setting the two-way valve to the engine position.
 13. The method of claim 12, further comprising: monitoring for an auto-stop mode, wherein the auto-stop mode occurs when the engine is not producing positive torque; if the engine is in the auto-stop mode and if the monitored ambient air temperature is below the calibrated cold ambient temperature, comparing the monitored transmission oil temperature to a calibrated second transmission temperature, wherein the calibrated second transmission temperature is less than the calibrated first transmission temperature; and if the monitored transmission oil temperature is below the calibrated second transmission temperature, setting the two-way valve to the transmission position. 